First you have to understand which are the ingredients that slow or halt cancers. It's the active compounds, THC and CBD, that seem to slow some and possibly cure some types of cancer. In the lab studies that have shown positive indications against cancer, those active ingredients have often been administered in much higher concentrations and doses to mice and/or rats than human users would obtain through smoking, eating, or vaping.

For human recipients, the by-products of combustion that come along with those active ingredients are still potentially carcinogenic (although I'm convinced the active compounds probably deliver some protective effects against those combustion byproduct carcinogens). So it's a subtle double-edged sword in a lot of ways and thus is hard for folks who want it to be either all good or all bad to understand. It's even hard for those of us who know it has both benefits and drawbacks to understand.